Catalytic extrusion of polylactide/ethylene vinyl alcohol bioplastic film

Abstract

The ring-opening polymerization of lactide was generated by a continuous single-step reactive extrusion process in the presence of 2-ethylhexanoic acid tin(II) salt, Sn(Oct)2, as a catalyst to obtain high molecular weight polylactide (PLA). For good practical applications of PLA, the softness of the PLA was modified via the graft copolymerization from poly (ethylene-co-vinyl alcohol) EVOH, which is a biocompatible, flexible and soft random copolymer. To investigate the chemical structure of the graft copolymer, the products were characterized by FTIR. The results show that the strong absorption emerged at 1740 cm-1 in the spectra of EVOH-g-PLA and pure PLA was identical, which assigned to carbonyl (C=O) in PLA. Therefore, these results could be confirmed that the ring-opening polymerization of lactide with EVOH by using catalytic extrusion was carried out successfully. Furthermore, the EVOH-g-PLA copolymers gave the number average molecular weight (Mw) ranging from 24.5x104 to 36.6x104 g/mol. The amount of graft copolymer and the grafting degree showed a maximum at catalyst content around 0.5 wt%. The optimized LA/EVOH content and the screw speed were 50/50 wt% and 40 rpm, respectively. Furthermore, the EVOH-g-PLA copolymers were fabricated into bioplastic films by compression moulding technique for morphological study by SEM and mechanical testing. The elongation of grafted PLA were improved significantly compared to pure PLA. The tradeoff included the reduction of tensile strength.